Ferrite with constricted magnetic hysteresis loop



June 1961 o. ECKERT 2,989,477

FERRITE WITH CONSTRICTED MAGNETIC HYSTERESIS LOOP Filed Nov. 14, 1956 2SheetsSheet 1 AYAYAYAV E5 5 NAVAAVVA 35 25' M W AMMAA .zfiwAAAAA/wAm/ WM A #1224; INVENTOR.

O. ECKERT June 20, 1961 FERRITE WITH CONSTRICTED MAGNETIC HYSTERESISLOOP 2 Sheets-Sheet 2 Filed Nov A AAA w TAAA INVENTOR.

0.12%? [CK 57- Maw BY WC United States Patent Ofice 2,989,477 PatentedJune 20, 1961 2,989,477 WITH CONSTRICTED MAGNETIC HYSTERESIS L001? OskarEckert, L'auf (Pegnitz), Germany, assignor to Steafit-MagnesiaAk'tiengesellschaft, Lauf (Pegnitz), Germany, a corporation of GermanyFiled Nov. 14, '1956, Ser. No. 622,198 Claims priority, applicationGermany Nov. 21, 1955 Claims. (Cl.252-'62.'5)

Ferromagnetic metals with constricted hysteresis loops (see, forexample, Bozorth, Ferromagnetism, published by Nostrand Co., Inc., 1951,pages 498 to 499), have, as is well known, at small field strengthwithin the constriction area, constant permeability, i.e., permeabilityindependent of the field strength equal to the initial permeability,very low hysteresis losses and, in general, small residual losses. Asindicated in the above cited literature, such materials may be subjectedto thermomagnetic treatment. By thermomagnetic treatment, in thisconnection, is meant the passing through a thermic cycle during thesimultaneous presence of a magnetic longitudinal or transverse field.The concept of longitudinal or trans verse field is, in this connection,to be understood as relative to the later measuring field; alongitudinal or transverse field, respectively, means that such field,during the thermomagnetic treatment, is parallel, respectively vertical,to the later measuring field. Through this type of treatment, theseferromagnetic materials display a substantial alteration of the form ofthe hysteresis loop, and hence a change of the magnetic properties.

This invention is based on the discovery that it is possible tomanufacture specific ferrites showing a constricted magnetic hysteresisloop which are, consequently, capable of thermomagnetic treatmentsimilarly as for metals.

The invention teaches the production of such ferrites of the copper-zincand copper-cadmium ferrite systems which can be subjected tothermomagnetic treatment of the above type, and are distinguished fromhitherto familiar ferrites by the fact that, under the samemanufacturing conditions, they have constricted hysteresis loops.

In accordance with the invention, ferrites with this characteristic inthe copper-zinc and copper-cadmium ferrite systems must have acomposition of at least 50 mol percent Fe O and a small addition ofcobalt oxide. The addition of cobalt oxide is suitably determinedbetween 0.1 and 5% by weight, calculated on the total basic batch of thecopper-zinc or copper-cadmium ferrite, expressed in metallic oxides. Theinvention has shown that it is particularly advantageous to choose thecobalt oxide content between 0.35 and 1.5% by weight, calculated on thebasic batch. The copper-zinc and copper-cadmium ferrites in question,which react strongly to the addition of cobalt oxide with a constrictedloop, cover, in the threecomponent system Fe O -NiO-ZnO the area definedin the attached diagrams of FIGS. 3 and 4 by the quadrangles A, B, C, D.The compositions at the corners in percent by weight, are:

The above ferrites may be prepared in the'usual way, either by joint orpartial precipitation, from correspond: ing metal salt solutions, or, asis customary, in ceramic,

arts, they may be prepared for further processing by wet milling andmixing of the respective metal oxides. The powdered mixtures thusobtained, after drying, maybe given the desired form either immediatelyby dry pressing, extruding, or similar methods, or it may be desirable,before ceramic forming, to proceed with a calcining firing of the entiremass or only a part thereof, preferably be-' tween 750 C. and 1200 C.The formed parts are sintered, depending on the composition, attemperatures between 1180 C. and 1350" C. To produce the constrictedhysteresis loop in ferrites, in accordance with invention, it isnecessary that the cooling takes place slowly, particularly in thetemperature range between 700 C. and room temperature. The cooling speedis dependent upon the volume of the fired body. As a criterion, it maybe stated that for a ring of about 46 mm. outside diameter, 34 mm.inside diameter, and 10 mm, height, the

cooling time from 700 C. to room temperature should take not less than12 hours. If the rings are cooled rapidly, the efiect of loopconstriction does not occur. However, the constriction may be regainedeven for rings' cooled too rapidly, by re-heating them to a temperatureof about 700 C., and cooling them slowly, as above described.

Examples of the invention follow hereafterz (a) For the systemCuO-ZnO-Fe O In a steel bal mill are ground together 412.5 g. Fe O 375g. CuO, 50 g. ZnO, 3.25 g. CoO.

(b) For the CuO-CdO-Fe O porcelain dish, and dried. The powder, thusobtained, is pressed, according to ceramic pressing techniques,- 'into;

rings having dimensions of 59 mm. outside diameter, 35.8 mm. insidediameter, and 12 mm. height, the amount of pressure applied being about0.5 to 1 t./cm. The ferrite raw-pieces, thus obtained, are sintered in akiln at 1320 C. for two hours, whereupon the heat is shut off. The ringsare cooled to room temperature in the kiln during a period ofapproximately 24 hours. The ferrite rings thus obtained are providedwith 0.4 mm. copper enameled wire with windings as primary winding, and,as secondary winding, further 200 windings with 0.2 mm. copper enameledwire are applied. In the oscillographic photograph of this ferrite,produced in accordance with the invention, which is shown in FIG. 2a,one can distinctly recognize the loop constriction of the hysteresisloop.

The following experiment proves that ferrites produced in accordancewith the invention are susceptible to thermomagnetic treatment:

A ferrite toroid as prepared in the examples with 100 windings as aprimary winding, is placed in a kiln. While heating to 600 C., and slowcooling for 12 hours to room system: In a steel ball mill 487.5 g. Fe O875 g. CuO, 25 g. CdO and 3.2-5 'g.-'

temperature, a longitudinal magnetic field is maintained by means of thering winding by l a. direct current, corresponding to a magnetic fieldstrength of about 15 a. windings/cm. If the hysteresis loop of theferrite after this thermornagnetic treatment is recorded in the same asdescribed above, the result is analogous to that of metals when they aresubjected to heat treatment in the longitudinal magnetic field; acomplete change of the form of the hysteresis loop takes place, as maybe seen in FIGS. la and 2b. In analogous manner, heat treatment in thetransverse magnetic field may be carried out with corresponding effect;(see the above cited book by Bozorth).

The technical progress obtained with such ferrites in accordance withthe invention, may be seen in the following: with thermic longitudinalmagnetization, for example, ferrites with distinctly rectangularhysteresis loop may be produced which are of importance to the entirefields of electronics and for magnetic amplification, for telephone andhigh-frequency fields; with thermic cross magnetization, ferrites ofhigh quality and a permeability independent of field strength may beproduced, which are particularly suitable for the field oftelecommunication.

I claim:

1. A ferrite with a constricted magnetic hysteresis loop selected fromthe systems consisting of the copper-, zinc-,

iron oxide system and the copper-, cadmium iron oxide system containinga small amount of cobalt oxide, the iron oxide in said ferritecomprising at least 50 mol percent of the composition expressed as metaloxides and containing about 62.5 to 91% by weight of ferric oxide, about1% to 30% by weight of CuO, about 0.1 to 5% by weight of C00, and theremainder consisting essentially of a metal oxide selected from thegroup consisting of ZnO and CdO.

2. A ferrite as defined in claim 1 containing between 0.35 and 1.5% byweight, of cobalt oxide.

3. A ferrite as defined in claim 2 in which the ferrite is of thecopper-, zinc, iron oxide system, the proportion, by weight of copperoxide, zinc oxide and iron oxide being within the area A-B-C-D of FIG. 3of the drawing, the corners of area A-B-C-D being as follows:

A=70% Fe 0 30% CuO, 0% ZnO, by weight,

B=70% Fe O 1% CuO, 29% ZnO, by weight,

C=91% Fe O 1% CuO, 8% ZnO, by weight,

=89% F8203, 11% CuO, 0% ZnO, by weight.

4. A ferrite as defined in claim 2 in which the ferrite is of thecopper-, cadmium-iron oxide system, the proportions by weight of copperoxide, cadmium oxide and iron oxide being within the area ABCD of FIG. 4of the drawing, the corners of area A,B,C,D, being as follows:

A=70% Fe O 30% CuO, 0% CdO, by weight, B=62.5% Fe O 1% CuO, 36.5% CdO,by weight, C=91% F6203, 1% CuO, 8% CdO, by weight, D=89% Fe O 11% CuO,0% CdO, by Weight.

5. A process for preparing ferrites selected from the class consistingof copper-zinc-iron ferrites containing copper, zinc and iron oxideswithin the limits defined by area ABCD of FIG. 3 of the drawing plus 0.1to 5% by weight of cobalt oxide and copper-cadmium-iron ferritescontaining copper, cadmium and iron oxides within the limits defined bythe area ABCD of FIG. 4 of the drawing plus 0.1 to 5% by weight ofcobalt oxide comprising preparing a powdered composition consistingessentially of ferric oxide, copper oxide, cobalt oxide and an oxideselected from the group consisting of zinc oxide and cadmium oxide inthe proportions required to provide an oxide mixture of a compositionwithin the areas specified with 0.1 to 5% by weight of cobalt oxide,molding said powder composition to shape, firing the molded body atabout 1180 C. to about 1350 C., and thereafter slowly cooling the firedbody from 700 C. down to room temperature over a period of at leastabout 12 hours to provide a ferrite body having a constricted hysteresisloop.

References Cited in the file of this patent UNITED STATES PATENTS2,549,089 Hegyi Apr. 17, 1951 2,565,861 Leverenz et a1. Aug. 28, 19512,646,608 Boeke July 28, 1953 2,656,319 Berge Oct. 20, 1953 2,723,239Harvey Nov. 8, 1955 2,736,708 Crowley Feb. 28, 1956 2,886,530 Greger May12, 1959 FOREIGN PATENTS 645,056 Great Britain Oct. 25, 1950 682,838Great Britain Nov. 19, 1952 735,375 Great Britain Aug. 17, 1955 OTHERREFERENCES Economos: J. American Ceramic Soc., July 1955, p. 242.

J. Institute of Electrical Engineers, Japan, November 1937, pp. 4, 5, 7;October 1939, p. 571; June 1939, pp. 276-279, 281.

Bozorth et al.: Physical Rev., September 15, 1955, pp. 1792, 1793.

Proceedings of the IRE, vol. 44, No. 10 (Ferrites Issue). October 1956,pages 1300, 1301, 1304, 105 and 1306.

Ferromagnetism," Bozorth, D Van Nostrand, 1951, pp. 498 and 499.

RCA Review, September 1950, p. 345.

1. A FERRITE WITH A CONSTRICTED MAGNETIC HYSTERESIS LOOP SELECTED FROMTHE SYSTEMS CONSISTING OF THE COPPER-, ZINC-, IRON OXIDE SYSTEM AND THECOPPER-, CADMIUM IRON OXIDE SYSTEM CONTAINING A SMALL AMOUNT OF COBALTOXIDE, THE IRON OXIDE IN SAID FERRITE COMPRISING AT LEAST 50 MOL PERCENTOF THE COMPOSITION EXPRESSED AS METAL OXIDES AND CONTAINING ABOUT 62.5TO 91% BY WEIGHT OF FERRIC OXIDE, ABOUT 1% TO 30% BY WEIGHT OF CUO,ABOUT 0.1 TO 5% BY WEIGHT OF COO, AND THE REMAINDER CONSISTINGESSENTIALLY